As is known, the coffee-based beverage is usually obtained by means of percolation of pressurised hot water which passes through a layer of coffee powder. The coffee powder is normally obtained by toasting and then grinding the coffee beans.
In professional espresso coffee machines, the coffee powder is placed inside a cavity of a filter holder and subjected to a light pressing action. Then the filter holder is positioned on a machine body which supplies the pressurised hot water to the cavity of the filter holder and the coffee-based beverage flows out of a spout.
There exist moreover a number of machines mainly for domestic use, but also for professional use, which envisage the use of capsules containing a predefined amount of coffee powder. This type of machine is very popular with users since the capsules containing predefined amounts offer numerous advantages compared to loose coffee powder. The main advantage is that it enables one to have a coffee powder which, packaged in a controlled atmosphere, maintains its organoleptic characteristics over long periods of time.
The main characteristics of the coffee beverage (espresso coffee) are: the aroma, the creaminess, the body and the aftertaste.
Some of these characteristics, such as the aroma, the body and the aftertaste, may be decided at the time when the type of coffee powder is chosen, while other characteristics, such as the creaminess, may be decided also during preparation of the coffee beverage.
In this connection some devices which help the user adjust the creaminess of a coffee-based beverage are known in the prior art. These devices essentially consist in a constriction of the spout through which the coffee beverage flows out. The constriction is generally obtained by means of a rigid element which is pushed by a spring against the opening of the spout. The operating principle is simple: the pressure of the beverage supplied opposes the action of the spring and displaces the rigid element from the spout opening, allowing the beverage to pass through. The greater the degree of prestressing of the spring, the higher the pressure of the beverage must be in order to overcome the force of the spring.
The constriction increases the creaminess of the coffee and the user, via prestressing of the spring, has the possibility of adjusting the degree of creaminess.
The prior art, although very popular, is not without drawbacks.
The system is complicated from the point of view of its constructional design, since it is necessary to provide an external element suitable for being screwed onto the spout, a rigid constriction element and a spring suitable for pushing the constriction element against the spout opening. The cleaning operation is not always easy to perform and in particular repositioning of the components of the device is not simple, in view of the relative mating between the spring and the rigid element.